A printer or a projection television requires light sources consisting of three colors of R (red), G (green), and B (blue). As the light sources, there has been developed a wavelength conversion laser that conducts second harmonic generation (SHG) by using a nonlinear material, in which laser beams of a 900 nm band, a 1 μm band, and a 1.3 μm band are each a fundamental laser beam. In the SHG, in order to realize a high conversion efficiency to the second harmonic laser beam from the fundamental laser beam, there is required an increased power density of the fundamental laser beam on the nonlinear material, and a high-brightness laser beam that has small wave aberration.
As a method for realizing the wavelength conversion laser device of this type, there is a second harmonic generation laser device within a laser resonator shown in FIG. 15 (for example, refer to Non-patent Document 1). The laser device shown in FIG. 15 includes a pumping semiconductor laser 101 that emits a pumping beam, an optical fiber 102 that transports the pumping beam, a focusing optical system 103 that condenses the pumping beam, a first mirror 105 that reflects the fundamental laser beam and transmits the pumping beam, a laser medium 104, a second mirror 106 that reflects the fundamental laser beam, a third mirror 107 that reflects the fundamental laser beam and transmits the second harmonic laser beam, a nonlinear material 109 that converts the fundamental laser beam into the second harmonic laser beam, and a fourth mirror 108 that reflects the fundamental laser beam and the second harmonic laser beam. Reference numeral 110 denotes a propagation configuration within the resonator of the fundamental laser resonator that is made up of the first mirror and the fourth mirror, and reference numeral 111 denotes an output of the second harmonic laser beam.
In FIG. 15, the pumping beam that is outputted from the pumping semiconductor laser 101 is transported through the optical fiber 102 and outputted. The pumping beam is then adjusted in the optical axis and the beam size so as to coincide with the fundamental propagation configuration 110, and focused by the focusing optical system 103, and absorbed by the laser medium 104. As a result, a gain occurs in the laser medium 104 with respect to the fundamental laser beam, and a resonator that is made up of the first mirror 105 to the fourth mirror 108 generates the laser oscillation of the fundamental laser beam.
In this event, the fundamental laser beam that has been inputted to the nonlinear material 109 is partially converted into the second harmonic laser beam, and outputted to the external as the second harmonic laser beam output 111 by the third mirror 107. The resonator that is made up of the first mirror 105 to the fourth mirror 108 is so structured as to obtain high-brightness laser oscillation with respect to the fundamental laser beam, and realizes high-brightness laser oscillation that is small in wave aberration. Also, as indicated by the propagation configuration 110, the beam size of the fundamental laser beam is reduced by the nonlinear material 109 to increase the power density of the fundamental laser beam, thereby realizing highly-efficient SHG.
Non-patent Document 1: Optics Communications 205 (2002), page 361, issued by Elsevier Corporation.